Thomas Hackner

Comparison of topologies to drive the machine of an automotive electrical power steering with higher voltage levels

A comparison between different inverter topologies has been carried out and their suitability assessed for application as a driver unit of the asynchronous machine for an automotive electrical power steering system. The proposed topologies provide higher voltage levels to the machine compared to the voltage levels obtained directly from the automotive electrical power net and also provide a reduced slope of the input current drawn from the automotive electrical power net by utilizing an additional double layer capacitor as integrated energy storage device. The comparison includes an inverter with additional boost converter, an inverter with integrated boost converter and a third topology with integrated boost converter and modified driving scheme. A detailed analysis has been performed to determine the overall losses and most suitable topologies have been built and tested to prove theoretical predictions. Experimental results are in good correlation with theoretical predictions.

Comparison of different winding schemes of an asynchronous machine driven by a multi-functional converter system

A comparison between different winding schemes has been carried out to optimize an asynchronous machine for an automotive electrical power steering system. The machine is driven from a multi-functional converter that consists of an inverter with integrated converter. This integrated converter provides an increased dc-link voltage to the inverter, but forces additional dc currents to flow through the machine windings. A detailed analysis is performed to describe the influence of the dc currents to the behavior of the machine and four most suitable winding schemes have been selected for the investigation. Results of the analysis demonstrate the requirement to carefully select the winding scheme when an asynchronous machine is operated from a multi-functional converter system. FEM simulations verify the results of the analysis. Four machines with different winding schemes have been built and tested together with the multi-functional converter. Experimental results are in close correlation with theoretical predictions.

Application of a floating H-Bridge converter to stabilize the automotive energy net

A floating H-Bridge converter is proposed to stabilize the automotive energy net against undesired voltage spikes and to limit the voltage range for the electrical loads. In comparison to classical converter topologies the proposed floating H-Bridge converter with integrated energy storage device provides lower switch-voltage stress and allows therefore the implementation of high-current low-voltage switching devices with lowest on-state resistance and very simple drive circuits. This low cost topology, which is connected in series to the loads, is analyzed for different operating modes. A full-size prototype converter was build and tested to prove the converter performance for the given application. Theoretical predictions are in good correlation with experimental results.

Optimization of the Winding Arrangement to Increase the Zero-Sequence Inductance of a Synchronous Machine With Multifunctional Converter Drive

An automotive electric-power-steering synchronous machine driven from a multifunctional converter has the advantage of increased system voltage. The integration of the boost converter in the inverter and the electrical machine leads to new requirements for the machine design due to dc currents and increased high-frequency ripple currents in the motor windings. In this paper, the ripple currents of a synchronous machine with a multifunctional converter are investigated. Three winding arrangements are analyzed and compared to reduce the ripple currents together with interleaved pulsewidth modulation. This paper contains finite-element simulations of the zero-sequence flux and analyses of the ripple currents with and without low-frequency ac modulation and, hence, when operated at high and low rotational speed. The magnitude of the ripple current depends on the zero-sequence inductance. By rearranging the coils in the stator slots, the zero-sequence inductance is significantly increased. Experimental results are correlating well with theoretical predictions and demonstrate that the phase and star-point ripple currents are almost halved.

Optimization of the winding arrangement to increase the leakage inductance of a synchronous machine with multi-functional converter drive

An automotive electric power steering synchronous machine has been optimized for operation with a multi-functional converter. The multi-functional converter system integrates an inverter to drive the motor and a front-end boost converter to increase the dc-link voltage. The integration leads to new requirements for the machine due to dc currents and increased high-frequency ripple currents in the motor windings. In this paper the high-frequency ripple currents of a synchronous machine with multi-functional converter are investigated and three winding arrangements are analyzed and compared to increase the leakage inductances and therefore to reduce the high-frequency ripple currents. The paper contains analyses of the high-frequency ripple currents with and without low frequency ac modulation and hence, when operated at high and low rotational speed. An interleaved switching scheme is implemented to reduce the high-frequency ripple currents and evaluated for the given application. Experimental results are in good correlation with theoretical predictions and demonstrate the reduction of the high-frequency phase and star-point ripple currents with the optimized winding arrangement.

A novel tri-state driver to improve the switching performance in automotive converter

A novel low cost tri-state driver is presented to reduce the overvoltage of the synchronous MOSFET in an automotive dc-dc converter. A third high-impedance state allows the MOSFET to be driven in the linear mode for a few nano seconds. The reverse recovery current of the body diode is therefore diverted and does not charge the junction capacitance. This leads to a reduced voltage stress of the MOSFET and an improved EMI behavior of the converter. The value of the overvoltage can be controlled with a simple voltage source in the gate circuit. An analysis has been done to predict the overvoltage dependent on the voltage of this voltage source. Prototypes with different MOSFETs were built and tested to prove theoretical predictions. The additional power losses caused by the operation in the linear mode are small in this application.

Impact of the automotive energy net impedance on the voltage-stabilization performance of a floating capacitor H-Bridge converter

A floating capacitor H-Bridge converter is proposed to stabilize the automotive energy net against undesired voltage spikes and to limit the voltage range for the electrical loads. In comparison to classical converter topologies the proposed floating H-Bridge converter with integrated energy storage device provides lower switch-voltage stress and allows therefore the implementation of high-current low-voltage switching devices with lowest on-state resistance and very simple drive circuits. In this publication the impact of the energy net impedance on the voltage stabilization performance and on the stability of the system is analyzed. Analyses are performed, a control method is proposed and results of a full-size prototype converter are shown to prove the converter performance for the given application. Theoretical predictions are in good correlation with experimental results.

Measurement technique to determine the impedance of automotive energy nets for stability analysis purpose based on a floating capacitor H-bridge converter

The complexity of electrical energy nets in modern cars is increasing rapidly due to the rising number of dc-dc converters and motor controllers. Multi-converter systems may lead to negative impedance instability that must be avoided in the automotive energy net under all circumstances, including faulty conditions such as a failure of batteries or other energy storage devices. Many stability criteria that have been developed during the last years for multi-converter systems are impedance based stability criteria. Impedance measurements therefore play an important role when investigating stability issues of multi-converter systems. In this paper a floating capacitor H-bridge converter is proposed as a simple measurement device for impedance measurements in automotive energy nets. The device can be easily implemented, provides small size and weight and is able to cope with the high dc currents required by the loads. A full-size prototype converter was built and tested to prove the performance for the given application. Theoretical predictions are in good correlation with experimental results.